Skip to main content

Full text of "Screening procedure for candidate fumigants for stored grain and grain products"

See other formats

May 1954 E-878 


United States Department of Agriculture 
Agricultural Research Service 
Entomology Research Branch 


By N. M. Dennis and W. K. Whitney, Stored-Product Insects Section, 
Biological Sciences Branch, Agricultural Marketing Service 

Each year many new chemicals are submitted to the Manhattan, 
Kans., station for testing as fumigants for stored grain and grain prod- 
ucts. It would be impractical and unwise to conduct large-scale tests 
with every compound so submitted for screening. The screening pro- 
cedure described herein is designed to establish the minimum lethal 
dosage of the candidate compounds, both in space and in commodities, 
and their performance under various conditions. By this procedure a 
candidate fumigant can be evaluated in the laboratory at normal atmos- 
pheric pressure. 

By use of this procedure not only may promising new fumigants be 
discovered, but dosages may be established for large-scale tests in 
warehouses and other storage facilities. 

Before tests are started to evaluate the candidate compound, its 
physical and chemical properties are reviewed. Many compounds may 
be eliminated because of objectionable odor, flammability, corrosive- 
ness to metal, deleterious effect on the viability of seed grain, or other 
objectionable properties. Also its toxicity to man is considered, and 
any necessary precautions in handling the fumigant are observed. 
Germination tests are conducted if the compound shows promise as a 

The confused flour beetle ( Tribolium confusum Duv.) and the rice 
weevil ( Sitophilus oryza (L.)) are used to determine the comparative 
toxicity of the fumigant being studied, as these species represent, re- 
spectively, the more resistant and susceptible types of insects infesting 
stored grain. 

It is essential to have the condition and age of the test insects as 
nearly uniform as possible. To provide a continuing supply, cultures 
are started at weekly intervals. The insects are reared in a uniform 
food medium under constant temperature (80° F.) and humidity (70 per- 
cent), and tested as adults. 

ass flasks and in empty glass 
fumigant's , and then in 

mmod. - . Before being exposes 
s are places -mesh screen cages 

.30 insects to a cage. The 
cag< s impregnated with h' affin to prevent 

the insects from boring into the 

The fui tit is first tested in a 20-liter flask ( \ glass tube 

through rubber s' • d to a glass stopcock out- 

!-:. I wo cages, containing insects h species separate , 

of the flask. uum (about 20 

the flask to 'ate introdu< • the nt. 

f liquid fumigant in a pipette is then held over the 
end of the glass tube ling from th« k, and n.- 

aing t: - i : allowing the vacuum to draw the fumi. to 

of 20 hours the insects are ex 1 for 

. As : k on possible recovery a sec ond ob 

made 5 days later. I n 3 to 5 rep! re 

mtil thi ethal dosage is determined. 

Digitized by the Internet Archive 

and 6 feet higVis used (t.. . J . sts oT 1 foot 

in 901 r %' ' sed 

h disks o: . M Ir^rTirnMed with paraffi . ;es 

• lining the test insects are su 

Is — 1 in m the n ., u ter, md 1 inrh from the top. 

A ; ^s-sampling tube is p. reside eacl to 

M isonite disk. Thr. 
hole in this disk 'lie Liquid fumig nl 

• ler. G 

I coi rat 

t. The mortalit 

milling fractioi 

: • 

- - 
nd th. .i top 

the I ■ 

l, the fun 
in// i ■ , be used, with ■ s% /-\ - ■ 


cylinders. In this way the minimum lethal dosage and the dispersion 
of the gas may be determined, and also the time required for aeration 
of a product after fumigation. 

All the fumigation tests are conducted in a room where a tempera- 
ture of 80° F. is thermostatically maintained. Small variations of the 
temperature during the exposure period are recorded, but usually they 
do not appreciably influence the results. 

Figure 1. --Wire-screen cages for the test insects. 

Figure 2.--A 20-liter flask with stopcock and sus- 
pended test cages. The amount of vacuum in the 
flask is being checked with a manometer prior to 
the introduction of a measured amount of fumigant. 


. :: - ■ 

- — 'Z 

- c 


— ■ e 

3 - a 

- - - 



- u - 


- — 

5 - 

Z ~ 




3 S '